Cycloolefins can be polymerized through the olefin structure to yield plycycloaliphatics, or through a ring-opening process to yield unsaturated linear polymers. The latter process has particular appeal since the resulting polymers are sulfur-vulcanizable. Examples of patents describing catalysts and catalyst combinations as well as processes for polymerizing cycloolefins include U.S. Pat. Nos. 4,002,815; 4,025,708, 3,853,830; 3,597,403; and 3,778,420.
A number of the catalyst systems which have been suggested in the prior art for preparing polymers of cyclicmonoolefins such as tungsten or molybdenum halides in conjunction with organoaluminum compounds provide linear polymers having a relatively high proportion of gel. More recently, another catalyst system has been discovered which produces linear polymers of cyclicmonoolefins which essentially are gel-free. For example, in U.S. Pat. No. 4,025,708 a solvent is used for the tungsten compound in the catalyst system along with a non-conjugated acyclic olefin has a molecular weight modifier allowing for improved process control and substantially gel-free cyclopentene homopolymers and copolymers.
Dicyclopentadiene is a readily available ethylene production by-product, but not as much consideration has been given in the prior art to homopolymers and copolymers of dicyclopentadiene. Generally it has been observed that the application of broad prior art teachings to the preparation of homopolymers and copolymers of dicyclopentadiene has not been successful and results either in little or no reaction occurring, or if a reaction does occur, the polymer produced is substantially insoluble in hydrocarbon solvents including aliphatic, cycloaliphatic and aromatic hydrocarbons. U.S. Pat. Nos. 3,853,830 and 4,002,815 describe processes for preparing substantially gel-free copolymers of cyclopentene with dicyclopentadiene utilizing a catalyst which comprises at least one compound selected from the group consisting of dialkylaluminum iodides, alkylaluminum diiodides and mixtures of trialkylaluminum compounds with elemental iodine, and at least one solvent-soluble or monomer-soluble tungsten compound along with a non-conjugated acyclic olefin. It generally has been reported such as in U.S. Pat. Nos. 4,025,708 and 4,002,815, that in the system described therein, conjugated olefins such as butadiene and isoprene were active inhibitors, and this is why the processes described in those patents required the use of non-conjugated acyclic olefins.